X-ray apparatus



Feb. 14, 1939. H. FRANKEET AL 2,146,889

' X-RAY APPARATUS Filed Feb. 9, 1954 2 Sheets-Sheetl Feb. 14, 1939. H.FRANKE ET AL 2,146,889

X-RAY APPARATUS Filed Feb. 9, 1934 2 Sheets-Sheet 2 Patented Feb. 14,1939 UNITED STATES alias Artur OFFICE X-RAY APPARATUS ApplicationFebruary 9, 1934, Serial No. 710,516

' In Germany February 22, 1933 8 Claims.

For interrupting the operating current of an X-ray tube when makingphotographs with short exposure time, a switch in the anode currentcircuit is not suitable, because an arc is formed when the contacts ofsuch a switch are separated, due to which the current does notimmediately drop to zero. Another drawback of such a switch is that ithas a very large size due to the fact that the contacts must beinsulated from each other for high tension, and the switch gap must besufficiently long that the breakingarc extinguishes. Furthermore. such aswitch must be operated by the intermediary of highly insulated meansand the contact members must have a large radius of curvature.

Therefore in most X-ray apparatus the tube is placed into operation bythe closure of a switch in the primary low-tension circuit of the high'tension transformer and the exposure is interrupted by opening thisswitch. For short exposures the influence of the transients caused bythe switching on of the transformer is quite pronounced. Thesecondary-voltage does not immediately follow its regular curve, butonly after a time interval of a few cycles and the amplitudes of thetransients due to switching-on are not always of the same order. Astabilizing resistance, temporarily inserted in the circuit, issometimes used to eliminate this difficulty, but for instantaneousradiographs the use of such a resistance brings about an unduelengthening of the exposure time.

Moreover the current in the primary circuit is in general comparativelylarge, especially when the loading time is short, and the switch musttherefore be designed for such large currents and must be of robustconstruction. This impairs the speed of operation. It is evident that asmall and light switching mechanism may operate faster than a big one.Particularly when a great number of exposures are to be made in rapidsuccession. for example when making radiographs of the stomach orcinematographic radiographs, a small, easily movable, and rapidly actingswitch is needed.

The invention has for its object to provide for a switching arrangementpermitting a quick and z pertialess switching-on and interruption of theoperating current of an X-ray tube.

Another object of the present invention is the provision of a switchingarrangement which permits a rapid succession of the exposures.

A further object of the present invention is the provision of aswitching arrangement in which a low tension switch is included in theanode circuit of the tube.

Other objects will appear from the following description.

It is known that the current of an X-ray tube may be controlled by thepotential of an auxiliary electrode. This auxiliary electrode may bearranged in the X-ray tube itself or in a valve connected in series withthe X-ray emitting tube.

In order to suppress on one hand the current 10 through the tube and onthe other hand to permit free passage for the electrons it is desirablethat both a negative and a positive potential can be given to theauxiliary electrode with respect to the cathode. Commutators have been15 used for this purpose. For example a method of controlling the anodecurrent of an X-ray tube is known in which a rotary reversing switchserves to apply a periodically varying potential to the auxiliaryelectrode.

According to our present invention a considerably simpler installationis obtained by employing a resistance inserted between the cathode andthe auxiliary electrode of a discharge gap through which the anodecurrent of the X-ray tube has to pass, this resistance being connectedin the circuit of the anode current.

Thereby a negative biasing voltage is applied to the auxiliaryelectrode. The use of a resistance connected in the same way is knownfor the purpose of keeping the current constant, or for preventing thecurrent from exceeding a predetermined value or for regulating thedimensions of the focus. In the latter case it is necessary that theauxiliary electrode be disposed in the X-ray emitting tube itself.

When the resistance is sufliciently great, a small anode currentproduces a voltage drop in the resistance which is suflicient to limitthe current to so small a value that no appreciable X- ray emissiontakes place. Accordingly to our invention the switch for timing theexposure is connected across this resistance.

The novel features of our invention will be best understood by referenceto the accompanying drawings and the following explanation thereof.

Figures 1-5 are schematic diagrams showing some examples of switchingarrangements according to our invention.

Figure 6 is a perspective view of a rotary 50 switch which may be usedfor establishing the necessary contact in an apparatus for making agreat number of radiographs in rapid succession.

Figure 7 is a schematic diagram of a modification of the arrangementsrepresented in Fig- 5::

ures 1-5 and differs mainly from the latter by the presence of a valvetube connected in series with the X-ray tube.

Fig. 8 is a circuit diagram of another embodiment of the invention, and

Fig. 9 is a schematic diagram of an apparatus especially adapted formaking single exposures of exact duration.

Like numerals in the drawings indicate corresponding parts.

Referring to Fig. 1 an X-ray tube I, having an anode 2 and anincandescible cathode 3, is connected to a source of high. tension 4 bymeans of the conductors 5 and 6. The conductor 6. leading to the cathode3 contains a resistance I. The cathode is connected to a source ofenergizing current 8 through conductors 9 and" Ill; The X-ray tube has,in addition to the anode 2' and the cathode 3, a control electrode IIforexamplein the form of a grid situated in the path of the dischargeand so designed that when asmall negative potential with respect to thecathode for instance 100 volts, is applied to it; the anode currentintensity is insufficient for producing X- raysto any appreciableextent. A suitable resistance is for example 50,000 ohms; The currentwill then be of the order of a few milliamperes.

A switch I2 is connected in multiple with resistance 1. Closing thisswitch will cause the potential' difference between thecontrol electrodeand the cathode to be reducedto-zero. The electrons emitted by cathode 3will then be permitted to-pass over'tothe anode 2- ina greater quantity,so that the current may sufiice for making an X ray exposure. At the endof the exposure time,,switch l2is again opened'and the tube current ispractically interrupted; When switch I2 is in its open position, thevoltage difference between its contacts is very small in comparison withthe working voltageof'the tube. Furthermore, this switch has tointerrupt only a light current, as, it is included in the high' tensioncircuit of the tube and not in a low tension supply circuit. The switchIZ-may, therefore, be of a simple and easily movable type, permitting avery quick switching; The cathode 3 of the tube is grounded at l3 inFig. 1, whereby the switch 12 is also grounded and may be operated byhand or by a grounded switching mechanismas usually employed in X-rayapparatus having their operating, switch in the low tension primarycircuit of a supply transformer.

In order to ensure a sufficient currentintensity, in Fig. 2, a source ofelectromotive force. in the form of a biasing battery l4 has been.connected between the control electrode H and resistance 1, with itsnegative terminal connected to, the latter. It is unnecessary that. thebattery llsupply cur.- rent hence its capacity may be small; drybatteries such as are used for anode currentsupply in radio receiving.sets" aresuitable for this" purpose. The positivebiasv may amount to afew hundred volts.

The current flowing through resistance 1 when switch I2'is open producestherein a potential drop that eliminates the positive bias of battery l42 Consequently the current limits itself because higher current wouldproduce a higher voltage drop andwouldcausethe potential of the controlelectrodeto-becomemore negative and the repulsive eifect on theelectrons emitted by the cathode to be greater. When resistance 1 isshort circuited by switch l2, the voltageof battery l4 alone acts on thecontrol electrode, so that the latter no longer acts as an obstruction,but as a boosting element.

In Fig. 3, instead of a battery, a condenser l5 serves for applying apositive charge to the control electrode II. This condenser is chargedup to a suitable voltage by a transformer winding I6 through arectifying element IT. The latter may be an electric discharge tube, butother types of rectifying apparatus, such as contact rectifiers may beused as well. The E. M. F. in transformer winding I6 is induced by thewinding l8 which isthe primary winding of a heating current transformerof which I9 is the secondary coil. The current to winding 18 is obtainedfrom an -A. C..network not shown in the figure.

The condenser and rectifying element may be dispensed with and analternating voltage may be applied to the control electrode, becauseduring the half cycles in which the anode of the X-ray tube is negative,the tube becomes currentless automatically. In Fig. 4 an arrangement isshown wherein a transformer winding 20 is connected between the controlelectrode I l and resistance 1. The transformer'of which winding 20'forms part has four coils, namely, a primary 2 I, a secondary 22, andtwo'additional coils 20 and 23. The primary winding 2| is supplied withcurrent from a network not shown in the figure. The secondary 22 is ahigh tension winding, and is connected by Wire 5 to the anode 2" of theX-ray tube I and by wire 6 throughresistance l to the cathode 3.Transformer winding 23 serves for energizing the cathode and isconnected thereto through wires 9 and I: Winding 20 is so arranged thatits end'connected' to the control electrode is positivesimultaneouslywith the anode 2 of" the X-ray tube. If winding 2|] doesnot bias the control electrode in the proper direction, the connectionsshould be interchanged. In this arrangement'the effect of the positivebias is smaller in the first and last part'of the active half" wavesthan when a constant positive potential is applied to the controlelectrode.

The arrangement shown in Fig. acts in almost the sameway as that of Fig.4'. The control electrode H is connectedto one of a pluralityof taps 24of 'the transformer winding 20' by wire 21. Thepositive bias isthus'derived from the high tension' transformer winding. The presence ofmore than one tap has the advantage that the positive-bias is regulable.

A signalling device 26 is included'in wire 21 for indicating thefiow ofgrid current over the control' electrode. This device is shown as asmall glow discharge tube but a small incandescent lamp maybe'used'instead thereof or a fuse may serve to prevent too great a gridcurrent.

TheXray tube is fully loaded as long as switch I2 is closed. Thearrangement described is very suitable for making cinematographicradiographs. Apparatus serving for this purpose comprises a mechanismfor conveying the film, and the number of exposures during one minutedepends on the-velocity with which the film travels. The film traveldevice may be made subservient to the movement of switch l2. Thereforethis switch is preferably constructed as a switch drum as shown inllig.6. This switch comprises a contact segment 28 mounted on the peripheryof a drum 29 rotatable on a shaft 30 and driven by the travel device ofa film apparatus not shown in the drawings. Two contact brushes 3| and32, connected by wires 33 and 34 respectively to the ends of theresistance 1 (see other figures), are provided with contact points whichslide over the switch valve.

drum 21 and which are electrically interconnected by the segment 28during its passage past the contact points. With the drum 29 rotatingwith constant velocity, the time during which the contact brushes 3| and32 are interconnected, which is the exposure time of the radiograph,would be invariable. In order to permit variations of this time, thedrum 29 is provided with a plurality of additional contact segments suchas 35 and 36, mutually differing in length. The contact fingers 3i and32 are mounted upon an internally threaded member 31 which can bedisplaced in axial direction of the rotating drum by means of a screwspindle 38 and a small handwheel 39. By turning the handwheel 39 one maymake the contact fingers 3| and 32 cooperate with any of the contactsegments 28, 35 or 36 and thereby vary the exposure time.

In the arrangements shown in Figs. 1-5 the control electrode is in theX-ray tube itself.

Fig. '7 shows an arrangement in which a valve tube 46 is connected inseries with the X-ray tube 5. The valve tube has an anode 4|, anincandescible cathode 42 and a control electrode 43. Anode 4| isconnected through wire 44 with one of the terminals of the source ofhigh tension 4, the other terminal being connected through wire 45 withcathode 3. Anode 2 of the X-ray tube is connected through wire 45 withone end of resistance l, the other end of this resistance beingconnected to cathode 42. Between that end of resistance 1 which isconnected to wire 46 and control electrode 43 is connected a suitablesource of positive grid bias 41, which may be either a battery as shownin Fig. 2 or some other voltage means. Cathode 42 is heated toincandescence by current supplied from a source 25.

The installation illustrated by Fig. '7 functions in a similar way asthose of Figs. 1-5, except that the anode current of the X-ray tubepasses two discharge gaps. When switch |2 is open a high voltagedifference occurs between the anode 4| and cathode 42 of the valve tube46. This high voltage may cause X-rays to be emitted from the The amountthereof is small since the current as above explained is limited by thegrid potential, but nevertheless it may be advisable to employ screeningmeans to make these rays harmless. Such screening means which arelocated so as to interrupt the X-rays leaving the valve, may beconstituted by a sleeve of lead glass or other material impermeable toX-rays as is cutomary practice in X-ray plants.

When the circuit arrangement according to the invention is to be usedfor making one single radiograph or radiographs with any givenintervals, it is desirable that the high tension and energizing currentare switched off during these intervals, in order to spare the tubes andother electrostatically loaded parts. In Fig. 8 the source of hightension is shown as in Fig. 4 as a high tension step up transformerhaving a, primary low tension winding 2| and a secondary high tensionwinding 22. The source of energizing current for the cathode is shown asa transformer having a primary winding 48 and a secondary winding i5.One end of winding 2| and one end of winding 48 are connected throughwires 49 and 56 respectively to a common main of an A. C. network, notshown in the figure. The other end of winding 2| and the other end ofwinding 48 are connected to the other main of the network through wires5| and 52 comprising switches 53 and 54.

For placing the tube into operation, switch 54 is first closed to makethe cathode attain its glow temperature. Then switch 53 is closed, hightension being thereby applied to the tube and finally when the momenthas come at which the exposure should be made switch I2 is temporarilyclosed. After the exposure is made switches 53 and 54 are opened. Thiscourse of operation thus requires the operation of three switches, whichis more or less complicated. In the arrangement according to Fig. 9therefore these various switching manipulations are made subject to themovement of one single switching device. This device comprises a contactarm 55 connecting wire 56 leading from the network 51 to contactsegments 58 and 59 and to one of the two contact segments 60 and 6|.

In its initial position the arm 55 is out of engagement with the contactsegments and no current can flow to the X-ray system. When the contactarm 55 is moved in clockwise direction it first engages the segment 60,then turning further it engages also the segment 59 and finally thesegment 53. Subsequently the arm 55 leaves segment 60 and stillcontacting with 58 and 59 it engages segment 6|. Before leaving thissegment the contact with segment 58 and then that with segment 59 isbroken after which the contact arm returns to its initial position.

The switch denoted in the previous figures by I2 is represented in thediagram of Fig. 9 by two 1 contact segments 62 and 63 connected throughwires 64 and 65 tothe ends of resistance 1 and a contact arm 66.Thiscontact arm carries a ferromagnetic core 61 which is drawn into amagnetic coil 68 when this is energized. When coil 68 is deenergized,the contact arm and ferromagnetic core acting as a pendulum move incounterclockwise direction and contact is made by arm 66 between thesegments 62 and 63 during the short time interval required for itspassage along these segments. If now a second coil 69 is energizedinstead of coil 68,-core 6'! is drawn into coil 69 and the pendulumtakes a second stationary positionv denoted by a dotted line.

The coils 68 and 69 are connected through wires "ill and H with thatmain of the network 5! to which are connected wires 49 and 50. The otherends of coils 68 and 69 are connected through wires 72 and E3 tosegments 60 and 6| respectively. Just as in Fig. 7 the arrangement ofFig. 9 comprises a valve tube 40 in series with X-ray tube The cathode42 of valve tube 40 is supplied with heating current by a transformerhaving a secondary winding 14 and a primary winding 15, the latter beingconnected in parallel with transformer winding 48,

It will be clear that the contact arm 55 when making one revolution,first switches on the current through coil 68, this current flowing fromone side of network 51 through wire 10, coil 68, wire 12, to segment 62over contact arm 55 and back through wire 56 to the other side of thenetwork. Coil 68 serves to pull the contact arm 66 into the left handend position, whilst contact arm 55 first switches on the heatingcurrent of both X-ray tube and valve tube 40 by closing the supplycircuit of transformer coils 48 and 15 and thereafter switches on theanode voltage of both tubes and 43 by closing the circuit of transformerwinding 2|. When the contact arm leaves segment 68 and engages segment6|, the current through coil 68 is interrupted and instead thereof acurrent flows from one side of network 5'! through wires 10 and 1|,coils 69, wire 13 to segment 6| and over contact arm 55 through wire56jback to the other side of the network. Contact arm 66 moves from itsleft hand terminal position to its right hand terminal position andmomentarily short-circuits resistance 1, so that the X-ray tube is fullyloaded during a short period'. Contact arm 55 being moved further thehigh voltage and heating current are switched off. At last the currentthrough coil 69 is interrupted when contact arm 55 leaves segment 6| andreturns to its initial position. The pendulum 66 no longer beingretained by coil 69 moves by gravity into the position whereby itinterconnects contacts 82 and 63, but this has no effect since thecircuits are deenergized.

- Within the scope of the present invention the switching devices 55 and66 may be designed in any suitable form; Fig. 9 merely being an exampleto illustrate the operation of such devices. If it is also desired tochange the exposure time in the apparatus shown in Fig. 9, the segments62 and 63 may be made shiftable, i. e., movable to points nearer thecoils 68 and 69 at which the velocity of the pendulum is less. On theother hand, the length of the pendulum arm may be changed so as to varythe velocity with which the contact arm 66 passes over the segments 62and 63.

If the control electrode is in the X-ray tube itself, it may beconstituted by the focussing device. The method of using the focussingdevice of an X-ray tube, which then must be insulated from the filament,as a control electrode is well known to those skilled in the art andfurther explanation as to the design of such tubes is believed to beunnecessary.

The switching device 55 is shown to act directly in the primary circuitof the high tension transformer. If need be a relay switch may beincluded, the exciting current of which is acted upon by switchingdevice 55.

What we claim is:

1. A high tension electric discharge tube having an envelope, an anode,an incandescible cathode and a control electrode, a high tensiontransformer having a primary low tension winding and a secondary hightension winding, an anode circuit for said tube including said hightension winding, a current supply circuit for said primary winding and aheating current supply for said cathode, a resistance included in saidanode circuit with one end connected to said cathode, an electricconnection connecting said control electrode to a point on the anodecircuit between the other end of said resistance and said anode, meansfor short circuiting said resistance dur-- ing a predetermined timeinterval, said means comprising a rotatable switch drum having aplurality of contact segments of different lengths, contact brushescooperating with said segments andstationary with respect to therotation of said switch drum, and means for selectively bringing eitherone of said segments into its cooperative position with said brushes.

2. In an X-ray installation for making a series of exposures at equalintervals, in combination, an electric discharge tube having anenvelope, an anode, a cathode, and a control electrode, a hightensionsupply circuit for said tube, a heatingcurrent supply for said cathode,a resistance included in said circuit with one end connected to saidcathode, a mechanically-operated switch to periodically short-circuitsaid resistance, and an electric connection between said controlelectrode and a point on said-high-tension circuit between said switchand said anode.

3. An X-ray installation comprising, a hightension discharge tube havingan envelope, an anode, an incandescible cathode and a control electrode,a high-tension supply transformer having a primary low-tension windingand a secondary high-tension winding, a current supply for said primarywinding, a heating current supply for said cathode, an anode circuit forsaid tube including said secondary winding, a resistance included insaid anode circuit with one end connected to the cathode and beingindependent of the heating circuit of the cathode, an electricconnection between the free end of said resistance and said controlelectrode and including a source of biasing voltage forming part of saidtransformer, the terminal of said source connected to said controlelectrode having the same polarity as the anode, and means forshort-circuiting said resistance during a predetermined time interval.

4. An X-ray installation comprising a hightension discharge tube havingan envelope, an anode, an incandescible cathode, and a controlelectrode, a high-tension supply transformer having a primarylow-tension winding and a secondary high-tension winding, a currentsupply for said primary winding, a heating-current supply for saidcathode, an anode circuit for said tube including said secondarywinding, a resistance included in said anode circuit with one endconnected to the cathode and being independent of the heating circuit ofthe cathode, an electric connection between said control electrode and apoint on said secondary Winding having a potential intermediate thepotentials of the ends thereof, and means for short-circuiting saidresistance during a predetermined time interval.

5. In combination, an X-ray tube having an envelope, an anode, acathode,and a control electrode, an impedance having one end connectedto said cathode, means for producing a high-tension voltage between saidanode and the free end of said impedance, means for positively biasingsaid control electrode with respect to said impedance when said anode ispositive with respect to the cathode, means for supplying heatingcurrent to said cathode, and switching means for short circuiting saidimpedance.

6. An X-ray installation comprising an X-ray tube having an envelope, ananode, a cathode, and a control electrode, a resistance having one endconnected to said cathode, switching means for short circuiting saidresistance, means for supplying heating current to said cathode, meansconnected between the other end of said resistance and said anode forsupplying high-tension anode current to said tube, means forestablishing a potential difference between said control electrode andsaid other end of said resistance, said control electrode beingpositively biased with respect to said resistance when said anode ispositive with respect to said cathode.

'7. In combination, a high-tension electric discharge tube having anenvelope, an anode, an incandescible cathode, and a control electrode, astep-up transformer having a primary low-tension winding, and asecondary high-tension winding having a tap connected to said controlelectrode, means for energizing said cathode, an operating circuit forsaid tube including said secondary winding, an impedance in saidoperating circuit with one end connected to said cathode and its otherend connected to said secondary winding, and a switch to bridge saidimpedance.

8. An X-ray apparatus for taking a series of exposures of predeterminedduration, comprising an X-ray tube having an envelope, an anode, anincandescible cathode, and a control electrode, a high-tensiontransformer having a low-tension primary winding and a high-tensionsecondary winding, an anode circuit for said tube including saidsecondary winding, means for energizing said primary winding, means forheating said cathode, a resistance included in said anode circuit withone end connected to said cathode, an electric connection connectingsaid control electrode to a point on the anode circuit between saidanode and the other end of said resistance, and switching means forshort-circuiting said resistance during periodically-occurring timeperiods of predetermined length.

HEINRICH FRANKIE.

HEINZ VOIGT.

